viii COMPARATIVE ANATOMY 



The theory of the mutual action and reaction of inheritance and 

 adaptation in the struggle for existence clearly explained the forces 

 at work in the production of biological phenomena. The facts them- 

 selves had already been set out in their wonderful array, and com- 

 parative anatomy had even arranged them with profound philosophical 

 judgment, but no mechanical explanation of them was forthcoming. 



Thomas Huxley in England, and Carl Gegenbaur in Germany, by 

 means of their well-known text-books of comparative anatomy, were 

 the first to succeed in revealing in detail the important transformation 

 which this mechanical explanation of morphological phenomena, by 

 means of the new theory of descent, had brought about in the 

 biological sciences. 



It was my happiness during the first twelve years of my occupancy 

 of a University chair in Jena, i.e. from 1861 to 1873, to have 

 Gegenbaur for my colleague and friend. My own attempts to give 

 the theory of descent its widest application in those sciences which 

 are comprised under the term biology owe muck to this stimulating 

 intercourse, and are embodied in my works : Die G-enerelle M&rplwlogu 

 (1866), Die Naturliche Schopfungsgeschichte (1868, 8th ed. 1889), and 

 Die Anthropogenic (1874, 4th ed. 1891). 



Oscar Schmidt's and Gegenbaur's text-books and my above-named 

 works all issued from the University in the small Thuringian town of 

 Jena, and from the same source has now appeared this text-book of 

 Professor Arnold Lang, formerly my distinguished pupil, and after- 

 wards and till quite recently my helpful colleague. Professor 

 Lang has here successfully carried out the very difficult task 

 of selecting the most important results from the bewildering mass 

 of new material afforded by the extensive researches of the last 

 decades, and of combining them with great judgment. Besides this 

 he has, more than any former writer, utilised the comparative 

 history of development in explaining the structure of the animal 

 body, and has endeavoured always to give the phylogenetic 

 significance of ontogenetic facts. Lastly, he has, by the clear 

 systematic reviews of the various classes and orders which precede 

 the anatomical account of each race, further facilitated the phylo- 

 genetic comprehension of complicated morphological problems, his 



